Background: Most composite indices of disease activity and response criteria in RA have been validated and compared in clinical trials rather than routine care. We therefore wanted to compare the performance of the DAS28, SDAI and CDAI activity indices, their activity states, their response criteria, and also compare with the ACR response criteria in an observational clinical setting.
Methods: Agreement between the criteria sets was investigated using kappa statistics in a non-randomized cohort of 1789 RA patients from southern Sweden, starting their first course of anti-TNF-treatment. Mean disease duration was 12 years. Completer analysis was used.
Results: Agreement between high, moderate and low activity states was moderate or substantial, with kappa = 0.5 or better for all criteria. Agreement between SDAI and CDAI disease states was > 90% in these categories with kappa > 0.8. DAS28 original and modified cut point remission had good agreement (kappa = 0.91). Agreement between responses was substantial at the overall/ACR20 level (about 95%, kappa = 0.7 or better) for all criteria. By contrast, agreement was poor between moderate and high level responses.
Conclusion: Disease activity states according to the various indices perform similarly and show substantial agreement at all levels except remission. Agreement between SDAI and CDAI states is excellent. Response criteria, applied at the individual patient level, are hard to interpret and show poor agreement, except at the lowest level of response. Thus, they should not be applied uncritically in clinical practice.